The present invention relates to management of floor control on a shared communication channel in the context of half-duplex communications implemented in a communication network composed of a plurality of interconnected sub-networks.
PTT (Push-To-Talk) half-duplex communication systems are very widespread, in particular in the context of communications in professional environments involving safety services (police, fire and rescue), building and civil engineering companies and industry. Communication systems of PTT type implement a conversation method of half-duplex type on a shared communication channel, meaning that the communication passes in both directions, but not simultaneously. Communication systems of PTT type use MAC (medium access control) mechanisms at link layer allowing implementing conversations between users having terminal devices interconnected by a communication network, so that only one user speaks at a time, the other users then listening to the one who has taken the floor.
So as to ensure that only one communication device takes the floor on the shared communication channel, various mechanisms are known. A mechanism known as floor control is in particular known, implemented at application layer. Such a floor control mechanism is thus applicable to transmission of audio-data, but also to transmission of video data, or even audiovisual data or data of another type.
Such a floor control mechanism is based typically on the use of a server from which each terminal device shall request authorization before being able to take the floor. This server is then responsible for managing conflicts in floor requests, namely for managing the situations in which a plurality of terminal devices request competing respective floor controls.
In practice, a terminal device wishing to take the floor sends a floor request to the server. This wish to take the floor emanates typically from a user by pressing on a dedicated button of the terminal device. The server receives said request and selects the terminal device to which the floor is granted from potential competing requests that are sent thereto. The server sends a floor-granting confirmation message (“Floor Grant”) to the terminal device that has been selected and a notification message representative of said floor-granting confirmation (“Floor Taken”) to the other terminal devices, which then switch to listening to the terminal device to which the floor has been granted. The terminal device to which the floor has been granted can then take the floor and the other terminal devices are invited to await release of communication to send a floor request. When the terminal device to which floor control has been granted has ended the communication, said terminal device sends a floor releasing request (“Floor Release”) to the server. The server then advises the other terminal devices that communication has been released, and that a new floor control can be implemented.
The communication network may be composed of a plurality of sub-networks interconnected by a communication link, e.g., a satellite link, involving high transmission latency between said sub-networks. This transmission latency is not insignificant in particular in view of the transmission latencies within the sub-networks. Because of this transmission latency, the server might then typically have to wait for long time periods after having received a floor request to determine whether one or more competing requests exist, in particular coming from a sub-network other than the one from which the floor request has been received. If the server does not wait for such time periods before deciding to which terminal device to grant the floor, the terminal devices closest to the server in terms of latency are favored and the floor control mechanism is unfair. The sub-networks may also involve very different transmission latencies.
It is then desirable, in these circumstances, to provide a solution that is fair whatever the location, in the communication network, of the terminal device issuing a floor request. It is also desirable to provide a solution that reduces the time for getting access to the floor, namely the period of time between the moment at which the terminal device requests the floor and the time at which said terminal device actually obtains floor grant, while limiting the risk of not complying with the chronology of actual attempts to take the floor (i.e., the risk that a user X who has chronologically attempted to speak before a user Y is heard by at least one other user Z after the user Y).
It is also desirable to provide a solution in which, when a terminal device has actually obtained floor grant, the data transmitted by said terminal device in the context of floor control are received substantially simultaneously by the terminal devices being listening.
It is also desirable to provide a solution that is simple to implement and at low cost.